1. Field of Invention
The present invention relates to a liquid vaporizer that vaporizes a liquid reagent.
2. Description of the Related Art
Treatment of a Wafer surface is generally carried out in the production of semiconductor devices in order to increase the adhesion of a resist liquid to the wafer. The treatment of the wafer surface is carried out by using a vaporizer to vaporize a liquid reagent that serves to convert the hydrophilic surface into a hydrophobic surface and by coating the wafer in a chamber. The vaporizer used in such a case vaporizes at normal temperature the liquid reagent for hydrophobization treatment that is stored in a storage tank by bubbling the liquid reagent with nitrogen gas, as described in Japanese Patent Application Publication No. H6-132209. The vapor of the liquid reagent vaporized at a normal temperature is transported from the storage tank into the chamber together with nitrogen gas by using, for example, a resin tube.
Since such a storage tank typically should be of a large size, it cannot be disposed in the vicinity of the chamber and is arranged at a remote location (for example, at a distance equal to or larger than 5 m from the chamber). The vapor of the liquid reagent is easily condensed inside the resin tube and is a cause of forming particles. Therefore, the heating of the resin tube for long-distance transportation of the vapor is required. Meanwhile, since the bubbling of the liquid reagent with nitrogen gas is carried out in the vaporization at a normal temperature, the severity of the condensation problem is increased and the liquid reagent is degraded due to exposure to the nitrogen gas.
In another method for vaporizing a liquid reagent, highly efficient vaporization is performed by increasing the surface area of the liquid reagent by converting the liquid reagent into mist. However, when such conversion into mist is used, the remaining mist is a cause of creating particles. Accordingly, a method for removing the remaining mist as foreign matter with a filter member such as a mesh has been suggested, as described in Japanese Patent Application Publication No. 2008-263244. A method using the separation function of meshes has also been suggested to separate a gas phase from a liquid phase with a mesh allowing only gases to pass therethrough in a gravity-free state (or under very small gravity) and to vaporize from the separation surface by vapor pressure created by heating, as described in Japanese Patent Application Publication No. H05-156448.
However an increase in size of a vaporizer in each of the abovementioned methods is unavoidable so that the vaporizer cannot be disposed in the vicinity of the chamber, and those methods are the same in that the heating of a long resin tube for transporting the mixed gas is required.